THE IMPORTANCE OF BINARY GRAVITATIONAL MICROLENSING EVENTS THROUGH HIGH-MAGNIFICATION CHANNEL

We estimate the detection efficiency of binary gravitational lensing events through the channel of high-magnification events. From this estimation, we find that binaries in the separation ranges of 0.1 less than or similar to s less than or similar to 10, 0.2 less than or similar to s less than or similar to 5, and 0.3 less than or similar to s less than or similar to 3 can be detected with similar to 100% efficiency for events with magnifications higher than A = 100, 50, and 10, respectively, where s represents the projected separation between the lens components normalized by the Einstein radius. We also find that the range of high efficiency covers nearly the whole mass-ratio range of stellar companions. Due to the high efficiency in wide ranges of parameter space, we point out that the majority of binary-lens events will be detected through the high-magnification channel in lensing surveys that focus on high-magnification events for efficient detections of microlensing planets. In addition to the high efficiency, the simplicity of the efficiency estimation makes the sample of these binaries useful in the statistical studies of the distributions of binary companions as functions of mass ratio and separation. We also discuss other implications of these events.